This paper compares the performance and features of five different tools for object-oriented simulation. Three of the tools (MODSIM II, SES/workbench, and Sim++) are commercial products that are targeted exclusively at simulation work. Also examined are simulations in Smalltalk-80 and our own, non-commercial C++ simulation library, called MOOSE (MITRE Object-Oriented Simulation Executive). For each of the tools, we discuss the support for simulation, the support for object-oriented design and the degree to which these areas are effectively integrated. We report the results of performance testing of the tools using six concise benchmarks, each devised to test a specific feature, and one larger simulation, devised to compare general performance. Also included are partial results on ERIC, an object-oriented simulation tool developed at Rome Laboratories.